Saturn's rings were identified in 1655 by Dutch astronomer Christiaan Huygens. Space probe photos have uncovered the true extent of the ring system. The E ring reaches all the way to Saturn's moon Titan, which orbits 750,000 miles (1.2 million kilometers) from the planet. The rings are named with letters, in alphabetical order according to when they were discovered. The moon Enceladus orbits within the E ring.

At 313 miles (504 kilometers) in diameter, Enceladus is one of Saturn's smaller major moons. It was discovered in 1789 by astonomer William Herschel.

Enceladus' icy surface is relatively young, since impact craters are prominent only on a portion of its surface in the northern hemisphere. Elsewhere, the moon has been resurfaced by active "water volcanoes." The smooth, icy plains of Europa are the most reflective surfaces in the solar system, and are composed of fine-grained ice.

In the southern hemisphere, Enceladus is marked by distinctive "tiger stripes." These ridges indicate where water from Enceladus' interior is escaping to the surface. The heat map (inset) shows that the tiger stripes are much warmer than the rest of the surface: minus 135 degrees Fahrenheit (minus 93 degrees Celsius), compared with minus 330 degrees Fahrenheit (minus 201 degrees Celsius) elsewhere.